Embryology - Development of the Spinal Cord, PNS, SS, MS

Question 1

Describe neurulation

Answer 1

formation of the neural tube - sides of the neural plate elevate to from neural grove which then fuse.

Question 2

what will the neural tube become?

Answer 2

brain and spinal cord

Question 3

what forms neural crest cells?

Answer 3

neuroectoderm as the neural tube is closing - migrate into underlying mesoderm.

Question 4

What do cranial neural crest cells form?

Answer 4

• bones, cartilage, fascia, ligaments and tendons of face and neck
• sensory ganglia, autonomic ganglia
• (shared) meninges, schwann cells, melanocytes

Question 5

What do spinal neural crest cells form?

Answer 5

• dorsal root ganglia, autonomic ganglia
• fibrous skeleton of the heart
• (shared) meninges, schwann cells, melanocytes

Question 6

What becomes the spinal cord?

Answer 6

neural tube caudal to 4th pair of somites

Question 7

What are the three different regions that form in the neural tube and give rise to the different areas of the spinal cord.

Answer 7

ventricular - contains neuroepithelium that gives rise to neurons and glia

mantle - have alar and basal plate which become horns

marginal - outermost, will contain axons

Question 8

What forms ventral motor horns and dorsal sensory horns?

Answer 8

neuroblasts

Question 9

What forms astrocytes and oligodendrocytes?

Answer 9

gliablasts

Question 10

Where does the spinal cord extend to at birth?

Answer 10

LV4-LV5

Question 11

In adults where does the spinal cord end?

Answer 11

LV1-LV2

Question 12

At what point does the vertebral cord extend the whole length of the vertebral column?

Answer 12

during the 3rd month of gestation

Question 13

What is the active movement of axon toward an end organ or target?

Answer 13

neuronal pathfinding - follows signals released from somatic mesoderm

Question 14

When do dorsal and ventral rami form?

Answer 14

when the somite splits into epimere (dorsal) and hypomere (ventral)

Question 15

What three things does a somite split into?

Answer 15

myotome - skeletal muscle
dermatome - area of skin innervated by one spinal nerve
schleratome - axial skeleton

Question 16

What results when vertebral arches of spinal cord fail to fuse?

Answer 16

spina bifida occulta

Question 17

What results when the vertebral arches of the spinal cord fail to fuse, involving the meninges and/or neural tissue?

Answer 17

spina bifida cystics

• spina bifida with meningocele
• spina bifida with meningomyelocele

Question 18

What results when the neural plate fails to elevate and fuse?

Answer 18

spina bifida with myeloschisis

Question 19

What is the process where the caudal have of schlerotome fuses with cranial half of neighbor to form the vertebral body?

Answer 19

resegmentation

Question 20

how do intervertebral disks form?

Answer 20

annulus fibrosis is formed from mesenchymal cells

nucelus pulposus formed from the notochord

Question 21

what does rearrangement of sclerotomes result in?

Answer 21

• myotomes spanning the intervertebral discs
• spinal nerves exit between contiguous vertebrae
• intersegmental arteries pass midway over vertebral bodies

Question 22

What do ribs form from?

Answer 22

originate from costal processes of the 12 thoracic vertebra

Question 23

What does the sternum originate from?

Answer 23

form from ventral somatic ventral mesoderm of a pair of vertical bands called the sternal bars. ribs grow to and attach

Question 24

What are two congenital causes of scoliosis?

Answer 24

asymmetric fusion of vertebra

half of vertebra doesnt form

Question 25

What syndrome is caused by lack of resegmentation leading to fused cervical vertebrae?

Answer 25

Klippel-Feil Syndrome

Question 26

Describe the difference between pectus excavatum and pectus carinatum?

Answer 26

both are cased by excessive rib growth - excavatum: sunk in - carinatum: protrudes out

Question 27

Describe myogenesis.

Answer 27

mesoderm cells differentiate into myoblasts primordial muscle cells) which elongate and fuse together to form myotubes. Becomes a muscle fiber with the formation of contractile filaments in the cytoplasm of myotube.

Question 28

What syndrome is characterized by absent/underdeveloped pectoralis muscles and syndactyly of the fingers possibly due to loss of blood supply to chest wall during development?

Answer 28

Poland syndrom

Question 29

What is the ectodermal thickening at the apex of the limb bud called?

Answer 29

apical ectodermal ridge (AER)

Question 30

When does limb bud formation occur?

Answer 30

``` upper = day 26/27 lower = day 27/28 ```

Question 31

During week 5 the ends of the limb buds begin to flatten and separate from limb bud. What is this structure called?

Answer 31

handplates or footplates

Question 32

How are digital rays formed?

Answer 32

through ones of apoptosis (upper 6th, lower 7th)

Question 33

How are joints formed?

Answer 33

joint cavity is formed by cell death and surrounding cells differentiate into joint capsule.

Question 34

What limbs rotate the most causing a twisting of the dermatome?

Answer 34

lower limbs

Question 35

Why do sensory nerves 'spiral' around limb while motor fibers are distributed through and dont follow dermatome innervation?

Answer 35

sensory nerves are 'pulled' into limb as it develops while motor nerves grow into limb with myotomes.

Question 36

What portion of myotome becomes flexor muscles? extensor?

Answer 36

``` anterior = flexor posterior = extensor ```

Question 37

What is it called when the limb is absent due to suppression of limb bud development?

Answer 37

Amelia

Question 38

What is it called when only part of a limb is absent due to arrest of limb bud?

Answer 38

Meromelia | - phocomelia is type involving absence of long bones

Question 39

shortness of digits?

Answer 39

brachydactyly

Question 40

fusion of two or more digits from insufficient apoptosis between digital rays?

Answer 40

syndactyly

Question 41

extra fingers and toes?

Answer 41

polydactyly

Question 42

absence of digit?

Answer 42

ectrodactyly

Question 43

What is cleft hand or foot?

Answer 43

absence of 3rd metacarpal as well as fusion of thumb to second digit, and fusion of 4th to 5th

Question 44

how is clubfoot caused?

Answer 44

caused by abnormal position of the foot leading to deformed development, often by the presence of too little amniotic fluid

Question 45

Why are amniotic membrane strips in the amniotic fluid a problem?

Answer 45

causes amniotic bands - encircle portions of the fetus cutting off blood supply and amputating limbs or digits